Image processing method, and image processor and storage medium thereof

Abstract

The present invention relates to an image processing method using the error diffusion method to prevent jumps in a highlight part and darkening in a shadow part at high resolution. The image processing method comprises a step of calculating an average value of density values of N×M (N, M>1) pixels, a step of adding the average value and a diffused quantization error value, a step of quantizing the addition result with a predetermined number of tones, a step of selecting a quantization pattern corresponding to the quantization result, and a step of calculating the diffused quantization error value from the quantization error. The error diffusion algorithm has flexibility in outputting dots. In other words, error diffusion processing is performed in N×M pixel units, and a plurality of quantization patterns are provided, and a quantization pattern is selected based on the quantization result. Therefore jumps in a highlight part and smears in a shadow part can be prevented, the tone maintenance characteristic unique to the error diffusion can be satisfied, and a smooth and sharp image can be obtained.

1. An image processing method for performing image processing on input images using an error diffusion method, comprising:
 a step of calculating an average value of density values of N×M (N, M>1) pixels; 
 a step of adding said average value and a diffused quantization error value; 
 a step of quantizing said addition result by a predetermined number of tones; 
 a step of selecting a quantization pattern corresponding to said quantization result; 
 a step of calculating said diffused quantization error value from a quantization error; 
 a step of calculating a density gradient of said N×M area; and 
 a step of selecting a quantization pattern from said quantization result and 
 said density gradient. 
 
   
   
     2. An image processing method for performing image processing on input images using an error diffusion method, comprising:
 a step of calculating an average value of density values of N×M (N, M>1) pixels; 
 a step of adding said average value and a diffused quantization error value; 
 a step of quantizing said addition result by a predetermined number of tones; 
 a step of selecting a quantization pattern corresponding to said quantization result; 
 a step of calculating said diffused quantization error value from a quantization error, wherein said selecting step comprises a step of selecting a quantization pattern corresponding to said quantization result from a plurality of quantization patterns which do not have an isolated dot. 
 
   
   
     3. An image processing method for performing image processing on input images using an error diffusion method, comprising:
 a step of calculating an average value of density values of N×M (N, M>1) pixels; 
 a step of adding said average value and a diffused quantization error value; 
 a step of quantizing said addition result by a predetermined number of tones; 
 a step of selecting a quantization pattern corresponding to said quantization result; 
 a step of calculating said diffused quantization error value from a quantization error; and 
 a step of performing pulse width modulation on said quantization pattern. 
 
   
   
     4. An image processor for performing image processing on input images using an error diffusion method, comprising:
 a memory for storing said input images; and 
 a processing unit for performing image processing on said input images, wherein said processing unit adds an average value of density values of N×M (N, M>1) pixels and 
 a diffused quantization error value, quantizes said addition result with a predetermined number of tones, calculates the density gradient in said N×M area, selects a quantization pattern from said result and said density gradient quantization, and calculates said diffused quantization error value from a quantization error. 
 
   
   
     5. An image processor for performing image processing on input images using an error diffusion method, comprising:
 a memory for storing said input images; and 
 a processing unit for performing image processing on said input images, wherein said processing unit adds an average value of density values of N×M (N, M>1) pixels and 
 a diffused quantization error value, quantizes said addition result with a predetermined number of tones, selects quantization pattern corresponding to said quantization result from a plurality of quantization patterns which do not have an isolated dot, and calculates said diffused quantization error value from a quantization error. 
 
   
   
     6. An image processor for performing image processing on input images using an error diffusion method, comprising:
 a memory for storing said input images; 
 a processing unit for performing image processing on said input images, wherein said processing unit adds an average value of density values of N×M (N, M>1) pixels 
 a diffused quantization error value, quantizes said addition result with a predetermined number of tones, then selects a quantization pattern corresponding to said quantization result, and calculates said diffused quantization error value from a quantization error, and 
 a pulse width modulation circuit which performs pulse width modulation on said quantization pattern. 
 
   
   
     7. A computer readable storage medium for storing a program to perform image processing on input images using an error diffusion method, wherein said program comprises:
 a program for calculating an average value of density values of N×M (N, M>1) pixels, and adding said average value and a diffused quantization error value; 
 a program for quantizing said addition result with a predetermined number of tones, and selecting a quantization pattern corresponding to said quantization result; 
 a program for calculating said diffused quantization error value from a quantization error; and 
 a program for calculating the density gradient in said N×M area, and selecting a quantization pattern from said quantization result and said density gradient. 
 
   
   
     8. A computer readable storage medium for storing a program to perform image processing on input images using an error diffusion method, wherein said program comprises:
 a program for calculating an average value of density values of N×M (N, M>1) pixels, and adding said average value and a diffused quantization error value; 
 a program for quantizing said addition result with a predetermined number of tones, and selecting a quantization pattern corresponding to said quantization result; 
 a program for calculating said diffused quantization error value from a quantization error; and 
 a program for selecting a quantization pattern corresponding to said quantization result from a plurality of quantization patterns which do not have an isolated dot. 
 
   
   
     9. A computer readable storage medium for storing a program to perform image processing on input images using an error diffusion method, wherein said program comprises:
 a program for calculating an average value of density values of N×M (N, M>1) pixels, and adding said average value and a diffused quantization error value; 
 a program for quantizing said addition result with a predetermined number of tones, and selecting a quantization pattern corresponding to said quantization result; 
 a program for calculating said diffused quantization error value from a quantization error; and 
 a program for performing pulse width modulation on said quantization pattern.